Switched DC-DC converters comprise a switchable power stage, wherein an output voltage is generated according to a switching signal and an input voltage. The switching signal is generated in a digital control circuit that adjusts the output voltage to a reference voltage. The switched power stage comprises a dual switch consisting of a high-side field effect transistor (FET) and a low-side FET, an inductance and a capacitor. During a charge phase, the high-side FET is turned on and the low-side FET is turned off by the switching signal to charge the capacitor. During a discharge phase the high-side FET is turned off and the low-side FET is turned on to match the average inductor current to the load current. The switching signal is generated as digital pulse width modulation signal with a duty cycle determined by a control law. The control law may be implemented by a PID compensator.
A digital control circuit for DC-DC converters is very well suited for high performance applications that require a good load transient behavior. Nonetheless, if the powered application runs in light load the digital control circuit has the disadvantage of consuming too much current and therefore the efficiency of the DCDC converter is negatively influenced. This results in poor light load efficiency. Because many applications run most of their time in light load conditions, this negatively affects the overall energy consumption. Therefore it is highly desirable to have better efficiency under light load conditions.